Photochemical method and device for volatile organic compound pollution control

ABSTRACT

A method for removing methane and non-methane volatile organic compound concentrations from a gas stream. The method includes exposing the target gas to a halogen gas and a light from a suitable light source having a wavelength sufficient to activate halogen gas to halogen radicals, wherein the halogen radicals react with the VOC in the target gas to provide the target gas with a removed concentration of VOC as well as a device including a reaction chamber for reacting the halogen radicals with the VOC in the target gas.

FIELD OF THE INVENTION

The present invention relates to a method and a device for air pollutioncontrol. In particular, the present invention relates to a photochemicalmethod and device for removing volatile organic compounds includingmethane from in a target gas and use of the device.

BACKGROUND OF THE INVENTION

Volatile organic compounds (VOC) include methane and non-methanefractions, the latter commonly abbreviated NMVOC. Many specific NMVOCsare hazardous air pollutants, and NMVOCs together with methane give riseto secondary effects including climate change and the formation of airpollution [Harnung 2012]. Air pollution is a global problem according tothe World Health Organization [WHO Ambient, WHO Indoor], the World Bank[WB 2016] and others, estimated to cause 3.3 million deaths annuallyfrom ambient air pollution [WHO Ambient] and 3.8 million from householdair pollution [WHO Indoor]. Climate change is a global problem accordingto the United Nations [IPCC 2013], the Catholic Church [Francis 2015],the U.S. Department of Defense [U.S. DoD 2014], etc.

Methane has a closed shell of eight valence electrons and is chemicallysimilar to a noble gas including physical properties such as a very lowboiling point, high ionization energy, and low polarizability [Atkins2013; NIST Chemistry Webbook]. This unique chemistry has a number ofconsequences. Methane is the least reactive of all hydrocarbons in theatmosphere, giving it the longest residence time and a large globalwarming potential (72) on a 20-year time scale [Harnung 2012]. This lowreactivity (low reaction rate coefficient) means that it is hard todestroy methane with gas phase radical reactions without burning it athigh temperature, and often methane is found at concentrations belowthat required to burn. In addition, burning may be undesirable, forexample if it cannot be controlled and/or there is a risk of explosion.In addition to being relatively inert chemically, the unique electronicstructure of methane means that it has very weak intermolecularinteractions [NIST Chemistry Webbook]. Methane spends very little timeon the surfaces of heterogeneous catalysts due to low affinity forsurfaces leading to inefficient reaction, and it is difficult to trapusing adsorbents in order to enhance concentrations.

There is a need for an efficient and cheap technology for methane andNMVOC emission control. Reaction and adsorption would be the most commonmethods of pollution control for methane and NMVOC at concentrationsbelow the combustion limit (ca 4.4%) [Kwiatkowski 2019].

In this scenario, Gas Phase Advanced Oxidation (GPAO) [Johnson 2009] isa method for cleaning air based on the hydroxyl radical. The technologygenerates gas-phase hydroxyl radicals that initiate the oxidation bybreaking the C—H bond of a wide range of VOCs. It has a number ofadvantages over traditional air purification methods [Adnew 2016], mostimportantly improved energy efficiency, but also reduced installationand running cost, and reduced waste stream. Current technologies basedon hydroxyl radicals [Johnson 2009], however, are not able to react withmethane in an efficient and fast way. Molecules such as propane,2-methylpentane or n-hexane would react hundreds to thousands of timesfaster than methane [Darnall 1976]. This clearly represents a downsidethat must be overcome in order to obtain sufficiently fast reactionswith methane in the gas phase. In GPAO, a short wavelength of light(high energy) is used to photolyse ozone, energy is lost as heat whenthe product oxygen atom reacts with water vapor or hydrocarbons to formthe hydroxyl radical, and hydroxyl is lost to side reactions. These sidereactions are also self-limiting to the process, constraining theconcentration of hydroxyl that can be formed in the system.

An English chemist/industrialist, Henry Deacon, invented the DeaconProcess in 1868. It uses a catalyst to convert hydrochloric acid intochlorine gas. 4HCl+O₂-(catalyst)->2Cl₂+2H₂O. The only change since thenis that people have developed different and better catalysts. One of thebest catalysts currently available is the ruthenium oxide catalystdeveloped by Sumitomo Corp.

SUMMARY OF THE INVENTION

The world has been faced with technical problems relating to removingmethane and/or NMVOCs from an airstream, for example an industrial ventor chimney or other point source, as required by emissions regulationsor concerns for neighbors or the environment, control of odor fromlivestock or fermentation, etc. Current technologies are often tooexpensive, inhibiting installation. Removing methane from an airstreamis also a priority because of concerns about pollution and climatechange. Methane is difficult to remove by homogeneous or heterogeneouschemical reaction or to separate by adsorption, due to its uniquechemistry. In particular, in industrial settings, such as miningindustries, the concentration of methane is higher relative to manyother point sources, and the flow of air is larger. Adaptations to theprocess are necessary for the conditions of larger flow and methaneconcentration. Also, higher capital cost can be justified by theincreased intensity and value of the process.

The present inventors provide a solution to these problems.

In a first aspect, the present invention relates to a method forremoving VOC concentrations in a target gas comprising VOC, the methodcomprising, optionally in a suitable reaction chamber, exposing thetarget gas to a halogen radical precursor, such as a halogen gas, and alight from a suitable light source having a wavelength sufficient toactivate the halogen radical precursor to halogen radicals, wherein thehalogen radicals react with the VOC in the target gas to provide thetarget gas with a removed concentration of VOC.

In a second aspect the present invention relates to a device forremoving VOC concentrations in a target gas comprising VOC, wherein thedevice comprises a) a reaction chamber for exposing the target gas to ahalogen gas and a light from a suitable light source having a wavelengthsufficient to activate halogen gas to halogen radicals; b) an inlet forreceiving the target gas; c) an outlet for releasing the target gas witha removed concentration of VOC; d) a light source for providing awavelength sufficient to activate halogen gas to halogen radicals; ande) optionally a filter and/or scrubber for decreasing or removingbyproducts, such as halogen acid, e.g., HCl, unreacted halogen, e.g.,chlorine, formaldehyde, CO, CO₂ before the target gas with the removedVOC concentrations leaves through the outlet.

In a third aspect the present invention relates to a system comprisingthe device of the second aspect.

Typically, the present invention relates to a system for removing VOCconcentrations in a target gas comprising VOC, wherein the systemcomprises a) a reaction chamber for exposing the target gas to a halogengas and a light from a suitable light source having a wavelengthsufficient to activate halogen gas to halogen radicals; b) an inlet forreceiving the target gas; c) an outlet for releasing the target gas witha removed concentration of VOC; d) a light source for providing awavelength sufficient to activate halogen gas to halogen radicals; e) ascrubber for decreasing or removing byproducts, such as halogen acid,e.g., HCl, unreacted halogen, e.g., chlorine, formaldehyde, CO, CO₂before the target gas with the removed VOC concentrations leaves throughthe outlet, wherein the scrubber extracts the halogen acid and convertsit into halogen gas via oxidation and in the presence of a catalyst; f)optionally a liquefaction section collecting unreacted halogen gas fromthe outlet; g) optionally a recycling system for recycling the halogengas from the outlet to the reaction chamber; h) optionally a recyclingsystem for recycling the halogen gas extracted from the scrubber to thereaction chamber. In one embodiment, two scrubbers are present fordecreasing or removing byproducts, such as halogen acid, e.g., HCl,unreacted halogen, e.g., chlorine, formaldehyde, CO, CO₂ before thetarget gas with the removed VOC concentrations leaves through theoutlet, wherein the scrubbers extract the halogen acid and converts itinto halogen gas via oxidation and in the presence of a catalyst.

In a further alternative aspect, the present invention relates to asystem for removing VOC concentrations in a target gas comprising VOC,wherein the system comprises a) a reaction chamber for exposing thetarget gas to a halogen gas and a light from a suitable light sourcehaving a wavelength sufficient to activate halogen gas to halogenradicals; b) an inlet for receiving the target gas; c) an outlet forreleasing the target gas with a removed concentration of VOC; d) a lightsource for providing a wavelength sufficient to activate halogen gas tohalogen radicals; e) optionally a liquefaction section collectingunreacted halogen gas from the outlet; f) optionally a recycling systemfor recycling the halogen gas from the outlet to the reaction chamber;g) a means for introducing oxygen and a catalyst into the reactionchamber downstream from exposing the target gas to a halogen gas and alight from a suitable light source having a wavelength sufficient toactivate halogen gas to halogen radicals, for converting halogen acid tohalogen gas, and a recycling system for recycling the converted halogengas to the reaction chamber.

In a further aspect, the present invention relates to a method forremoving VOC concentrations in a target gas comprising VOC, the methodcomprising, optionally in a suitable reaction chamber,

-   -   i) exposing the target gas to a halogen radical precursor, such        as a halogen gas, and a light from a suitable light source        having a wavelength sufficient to activate the halogen radical        precursor to halogen radicals, wherein the halogen radicals        react with the VOC in the target gas to provide the target gas        with a removed concentration of VOC,    -   ii) optionally leading the target gas through a scrubber for        decreasing or removing byproducts, and converting halogen acid        to the halogen radical precursor, e.g. halogen gas, and        recycling the halogen radical precursor extracted from the        scrubber to provide the halogen radical precursor to the        suitable light source,    -   iii) optionally, collecting unreacted halogen radical precursor        by liquefaction, and recycling the halogen radical precursor to        the suitable light source; and    -   iv) providing the target gas with the removed VOC        concentrations.

In one embodiment, VOC is methane. In another embodiment, VOC is NMVOC.

In a further embodiment, the VOC in the target gas is selected from aprimary and/or secondary radiative forcing agents (greenhouse gases),such as hydrocarbons, in particular methane.

In a further embodiment, the target gas polluted with methane and/orNMVOCs is ambient polluted air, air in livestock barns, fugitiveemissions etc.

In a still further embodiment, elements of the target gas (e.g.chemically active substances or larger particles) that may damage thedevice or destroy or inhibit the action of the halogen gas are removedbefore being exposed to the halogen gas. Typically, the target gas isled through a prefilter to remove the substances or the larger particlesfrom the target gas before being exposed to the halogen gas.

In a further embodiment, the halogen radical precursor is a halogen gas.

In a still further embodiment, the halogen radical precursor, such asthe halogen gas, is present in a concentration in an amount which is atleast at the stoichiometric level in relation to methane and/or NMVOCsconcentration in the target gas.

In a further embodiment, the filter is present for decreasing orremoving byproducts, such as halogen acid, e.g., HCl, unreacted halogen,e.g., chlorine, formaldehyde, CO, CO₂ before the target gas with theremoved VOC concentrations leaves through the outlet.

In another embodiment, the scrubber is present for decreasing orremoving byproducts, such as halogen acid, e.g., HCl, unreacted halogen,e.g., chlorine, formaldehyde, CO, CO₂ before the target gas with theremoved VOC concentrations leaves through the outlet. In a particularembodiment, the halogen acid is converted to the halogen gas andrecycled to the reaction chamber bypassing the outlet. Examples of suchconversion is the Deacon reaction or the bleach reaction, see forinstance FIG. 6 . When converting the halogen gas, such as chlorine gas,using catalyzed Deacon reaction, such as the ruthenium oxide catalyzedprocess developed by Sumitomo Corp, oxygen is supplied from theatmospheric air, however, using pressure swing absorption, pure oxygencan be extracted from the air, and pure oxygen is a preferred optionover the use of pure atmospheric air.

The target gas with a removed concentration of VOC leaving the outletmay still contain unreacted halogen gas, which is trapped bycondensation. Excessive amounts of halogen gas leaving the outlet areunwanted in large industrial scale such as mine exhaust. Thus, in apreferred embodiment the unreacted halogen gas leaving the outlet isrecycled to the reaction chamber. This reduces environmental impact andmaterial streams/running costs. The halogen gas is preferably trapped byliquefaction, such as chlorine gas is trapped by chlorine liquefaction.

Thus, for an optimal large-scale process the chlorine gas is convertedfrom HCl, and the chlorine gas leaving the outlet are recycled to reactwith methane after being activated to halogen radicals.

In another embodiment, there is no filter or scrubber present.

When no filter or scrubber is present, an alternative is to apply theDeacon reaction such as embodied in the ruthenium oxide catalyzedprocess developed by Sumitomo Corp., on the entire airstream. Thus, in afurther embodiment, when no filter or scrubber is present, the halogenacid is subjected to oxygen and a catalyst, such as ruthenium(IV)oxidein the reaction chamber (illustrated in FIG. 7 ).

An alternative to applying the Deacon reaction to the halogen acidformed is to include at least two scrubbers. Thus, one embodiment, is tolet the target gas through two scrubbers for decreasing or removingbyproducts, such as halogen acid, e.g., HCl, unreacted halogen, e.g.,chlorine, formaldehyde, CO, CO₂ before the target gas with the removedVOC concentrations leaves through the outlet. The above-describedembodiments when the halogen acid is converted to the halogen gas andrecycled to the reaction chamber bypassing the outlet applies to one orboth scrubbers (illustrated in FIG. 9 ).

In a still further embodiment, the halogen gas is selected from chlorineand bromine gas, in particular chlorine gas. The chlorine gas ispurchased or produced on site using electrolysis of saltwater or is partof other gases containing chlorine that can be photolyzed.

In a further embodiment, the wavelength is from 540-180 nm, such as400-300 nm, for instance 380-320 nm, in particular from 370-350 nm.

In a still further embodiment, the light source is selected from afluorescent lamp, an LED lamp, an incandescent lamp, a gas dischargelamp, sunlight, or combinations hereof. In particular LED lamps arepreferred, and here the optimum photolysis is achieved at a wavelengthof approximately 365 nm in the range 300 nm to 400 nm (illustrated inFIG. 8 ).

One of the main products coming out of the methane oxidation (methaneremoval) is carbon monoxide. This is undesirable, and therefore it maybe useful to convert it to CO₂ using a catalyst. Thus, in a furtherembodiment, the CO formed during methane removal is subjected to acatalyst such as a supported platinum or palladium catalyst,alternatively rhodium and ruthenium, at a suitable temperature (150 to600° C. depending on catalyst preferably 300° C.) with integratedthermal management, to oxidize the CO to CO₂. In particular, the COformed during methane removal and present in the target gas with aremoved concentration of VOC leaving the outlet.

In a further embodiment, the concentrations of VOC in the target gas arebelow the combustion limit.

In a still further embodiment, the concentrations of methane and/orNMVOCs in the target gas are below the combustion limit. Typically, thetarget gas comprises methane in a concentration from 1.8 ppm to 5%(50000 ppm).

In another embodiment, the concentrations of VOC in the target gas areabove the combustion limit.

In a further embodiment, the concentrations of methane in the target gasare above the combustion limit; such target gases could be found in acoal mine, waste disposal site, or oil formation. Typically, the targetgas comprises methane in a concentration of at least 4.4%, such as from4.4 to 50%.

In a still further embodiment, the suitable reaction chamber is presentand has an inlet for receiving the target gas, a reaction zone whereinthe target gas is reacted with halogen radicals to remove VOC, such asmethane and/or NMVOCs, concentrations in presence of a suitable lightsource, optionally a system to increase the light source pathway (e.g.mirrors), optionally a filter or scrubber, and an outlet providing thetarget gas with the removed concentration of VOC.

In a further embodiment, the target gas with the removed concentrationof VOC, such as methane, is transported through a filter or scrubber todecrease or remove halogen acid, e.g., HCl, unreacted chlorine,formaldehyde, CO, CO₂.

In a still further embodiment, the suitable reaction chamber is presentand has an inlet for receiving the target gas, a reaction zone whereinthe target gas is reacted with halogen radicals to remove the VOCconcentrations, optionally a system to increase the irradiation pathlength e.g. by using reflective surfaces, optionally a filter orscrubber, and an outlet releasing the target gas with the removedconcentration of VOC.

In a further embodiment, ozone gas in a suitable carrier gas, such asair, is added into the reaction chamber in a suitable concentration toconvert a hydrogen halide (including HI, HBr and HCl) to volatile and/orphotolabile halogen species. In relation to the term “suitable carrier”comprising ozone gas this is known to the skilled person, and includesamong others air, nitrogen (N₂) and oxygen (O₂).

In a still further embodiment, fluid ozone, such as liquid or gas ozone,is added into the reaction chamber in a suitable concentration toconvert halogenic (or other halogen species in oxidation state I) tovolatile and/or photolabile halogen species.

In a further embodiment, elements of the target gas, such as dust,corrosive species and ammonia and other bases that may harm the device,destroy the halogen gas or otherwise interfere with the function areremoved before being exposed to the halogen gas.

In a still further embodiment, the target gas is led through a prefilterto remove larger particles from the target gas before being exposed tothe halogen gas.

In a further embodiment, the reaction chamber is present, and thechamber comprises two compartments, one first reaction compartment and asecond compartment, a filter/packed bed separating the first and secondcompartment, wherein the target gas after reaction in the firstcompartment is transported through the filter/packed bed into the secondcompartment wherein the target gas with the removed concentration of VOCis exposed to water which reacts with halogenic acid to form halogenthat is recycled to the reaction compartment.

In a further embodiment, a reaction chamber is present, and the chambercomprises two compartments, one first gas phase reaction compartment anda second compartment containing a scrubber wherein the target gas, afterreaction in the first compartment, is transported through the scrubberwherein the target gas is exposed to a liquid medium which reacts withthe hydrogen halide to form aqueous halide and halogen in thezero-oxidation state that is recycled to the reaction compartment.

In a third aspect, the present invention relates to a method forremoving methane and/or NMVOCs concentrations in a target gas comprisingmethane and/or NMVOCs as described in the first aspect, wherein thedevice additionally comprises a recycling element for recycling halogenradical precursor regenerated from the hydrogen halide gas formed duringthe reaction, to the reaction chamber.

In a further embodiment, the second aspect of the present inventioncomprises a recycling element for recycling halogen gas regenerated fromthe halogen acid gas formed during the reaction, to the reactionchamber.

In a fourth aspect the present invention relates to use of the device ofany one of the first, second and third aspects and any embodimentshereof for removing VOC, e.g. methane or NMVOC, concentrations in atarget gas comprising VOC.

Further objects and advantages of the present invention will appear fromthe following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described more fully with reference to theappended drawings illustrating typical embodiments of the invention.These drawings are by no means limiting the scope of the presentinvention and are only intended to guide the skilled person for betterunderstanding of the present invention.

FIG. 1 illustrates a photochemical air purification according to thepresent invention.

FIG. 2 illustrates a photochemical air purification withrecycling/recirculation according to the present invention.

FIG. 3 illustrates an air purification system, in line with ventilationsystem, for use in livestock barn according to the present invention.

FIG. 4 illustrates a System for capturing and destroying methane fromfugitive sources according to the present invention.

FIG. 5 illustrates a System for removing methane from ambient airaccording to the present invention.

FIG. 6 illustrates a system of the present invention suitable for use ina larger scale industry.

FIG. 7 illustrates a system of the present invention where the scrubberis removed and replaced by applying the Deacon reaction during themethane removal process.

FIG. 8 illustrates the choice of LED wavelengths.

FIG. 9 illustrates the system of the present invention using twoscrubbers.

FIG. 10 illustrates a model of the photochemical reactions.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors provide a solution to sluggish methane and/orNMVOCs reactivity in the gas phase and therefore to methane and/orNMVOCs emission control.

The gas phase and heterogeneous phase halogen reactors are able tocontrol air pollution including methane and other gases by takingadvantage of the faster rate of Cl radical reactions with manypollutants relative to many other radicals (OH, NO₃, ¹O₂, O₃ . . . ),and by taking advantage of the lower energy required to generate Clradical relative to for example OH radical, as well as by takingadvantage of the higher concentration of Cl radicals that can bemaintained relative to other radicals due to the nature of theself-limiting reactions in those systems. The examples are given for Cl,but apply also to Br.

The present invention is a fast and inexpensive method for destroyingmethane air pollution e.g. at concentrations below theexplosion/combustion limit. This range of concentrations includes manyof the most important fugitive sources of methane, such as withlivestock, biogas production, water treatment plants, landfills, oil andgas wells (including abandoned wells), coal mines (including abandonedcoal mines), melting permafrost and similar sources in nature. Moreover,the method of the present invention destroys non-methane VOC species,which are also powerful (primary and secondary) greenhouse gases, andboth primary pollutants in their own right and cause harmful secondarypollution. Furthermore, the method of the present invention providesgood volumetric energy efficiency (measured for example in kJ/m³ ofair), low maintenance, and it addresses odor issue, e.g., in livestockproduction and short treatment time, resulting in a compact system ableto treat a large stream of air as expressed for example in the spacevelocity metric.

Although exposing the target gas to a halogen gas and a light from asuitable light source having a wavelength sufficient to activate halogengas to halogen radicals may be performed in larger confined areas orsemi-enclosed areas, reaction preferably takes place in a suitablereaction chamber.

Preferably, the present invention relates to a system for removingmethane from a target gas comprising methane, wherein the systemcomprises a) a reaction chamber for exposing the target gas to chlorinegas and a light from a suitable light source having a wavelength from300 nm to 400 nm, sufficient to activate chlorine gas to chlorineradicals; b) an inlet for receiving the target gas; c) an outlet forreleasing the target gas with a removed concentration of methane; d) thelight source for providing the wavelength sufficient to activate halogengas to halogen radicals; e) a scrubber for decreasing or removing HCl,before the target gas with the removed methane concentrations leavesthrough the outlet, wherein the scrubber extracts the HCl and convertsit into chlorine gas via oxidation and in the presence of a catalyst; f)optionally a liquefaction section collecting unreacted chlorine gas fromthe outlet; g) optionally a recycling system for recycling the chlorinegas from the outlet to the reaction chamber; h) optionally a recyclingsystem for recycling the chlorine gas extracted from the scrubber to thereaction chamber.

In a further alternative aspect, the present invention relates to asystem for removing methane from a target gas comprising methane,wherein the system comprises a) a reaction chamber for exposing thetarget gas to chlorine gas and a light from a suitable light sourcehaving a wavelength from 300 nm to 400 nm, sufficient to activatechlorine gas to chlorine radicals; b) an inlet for receiving the targetgas; c) an outlet for releasing the target gas with a removedconcentration of methane; d) the light source for providing thewavelength from 300 nm to 400 nm; e) optionally a liquefaction sectioncollecting unreacted chlorine gas from the outlet; f) optionally arecycling system for recycling the chlorine gas from the outlet to thereaction chamber; g) a means for introducing oxygen and a catalyst intothe reaction chamber downstream from exposing the target gas to chlorinegas and the light from the suitable light source having the wavelengthfrom 300 nm to 400 nm, for converting HCl to chlorine gas, and arecycling system for recycling the converted chlorine gas to thereaction chamber.

In a further aspect, the present invention relates to a method forremoving methane concentrations in a target gas comprising methane, themethod comprising

-   -   i) exposing the target gas to chlorine gas, and a light from a        suitable light source having a wavelength from 300 nm to 400 nm        sufficient to activate the chlorine gas to chlorine radicals,        wherein the chlorine radicals react with the methane in the        target gas to provide the target gas with a removed        concentration of methane,    -   ii) optionally leading the target gas through a scrubber for        decreasing or removing byproducts, and converting HCl to the        chlorine gas, and recycling the chlorine gas extracted from the        scrubber to provide the chlorine gas to the suitable light        source,    -   iii) optionally, collecting unreacted chlorine gas by        liquefaction, and recycling the chlorine gas to the suitable        light source; and    -   iv) providing the target gas with the removed VOC        concentrations.

In a still further aspect, the present invention relates to a method forremoving methane concentrations in a target gas comprising methane, themethod comprising

-   -   i) exposing the target gas to chlorine gas, and a light from a        suitable light source having a wavelength from 300 nm to 400 nm        sufficient to activate the chlorine gas to chlorine radicals,        wherein the chlorine radicals react with the methane in the        target gas to provide the target gas with a removed        concentration of methane,    -   ii) leading the target gas through a scrubber for decreasing or        removing byproducts, and converting HCl to the chlorine gas, and        recycling the chlorine gas extracted from the scrubber to        provide the chlorine gas to the suitable light source,    -   iii) collecting unreacted chlorine gas by liquefaction, and        recycling the chlorine gas to the suitable light source; and    -   iv) providing the target gas with the removed VOC        concentrations.

The terms “decrease”, “decreased”, “removal”, and “decreasing” as usedherein as regards removing methane and/or VOC means the abatement,reduction, eradication, destruction, or conversion of methane and/or VOCin order to lower the concentration of methane and/or VOC in the targetgas after the reaction with the halogen radicals, such as in the deviceof the present invention, relative to the target gas before the reactionwith the halogen radicals, such as before introduction into the deviceof the present invention. The removal may be 100% (volume), such as atleast 90%, at least 80%, at least 70%, at least 60%, at least 50%, atleast 40%, at least 30%, at least 20%, at least 10%, such as from 10 to100%. All percentage (%) are considered individual embodiments of thepresent invention. Thus, for instance in one embodiment, the presentinvention relates to a method for removing from 10 to 100% VOCconcentrations in a target gas comprising VOC, the method comprising,optionally in a suitable reaction chamber, exposing the target gas to ahalogen radical precursor, such as a halogen gas, and a light from asuitable light source having a wavelength sufficient to activate thehalogen radical precursor to halogen radicals, wherein the halogenradicals react with the VOC in the target gas to provide the target gaswith a removed concentration of VOC.

The term “volatile organic compounds” as used herein and alsoabbreviated VOC means both methane and non-methane VOC (i.e. NMVOC) forexample aromatic and aliphatic hydrocarbons, ammonia and organicmoieties including heteroatoms such as N, S, and/or 0, such as selectedfrom a primary and/or secondary radiative forcing agents (greenhousegases), such as hydrocarbons, in particular methane.

The term “a suitable reaction chamber” as used herein means any reactionchamber having at least one inlet and at least one outlet andconstructed of a material that is not degraded by the halogen gas and/orthe light and/or the halogen radicals, such as glass reaction chambersand/or plastic reaction chambers, optionally equipped with mirrors orother optical devices to concentrate and increase the pathway of thelight source.

The term “a suitable light source” as used herein means any light sourcethat can generate light of a wavelength sufficient to remove theconcentration of one or more VOCs, such as methane, in the target gas,such as ambient air, in particular ambient polluted air. Typically, thelight source is selected from one or more of a fluorescent lamp, an LEDlamp, an incandescent lamp, a gas discharge lamp, sunlight, etc.Typically, the wavelength is from 540-180 nm, such as 400-300 nm, forinstance 380-320 nm, in particular from 370-350 nm.

The term “target gas” as used herein means any gas, such as air, inparticular ambient air, comprising at least methane, but typically alsoother VOCs, such as NMVOCs, in concentrations of at least 1.8 ppm.Typically, the target gas comprises methane and VOCs in concentrationsthat should be decreased and/or removed completely or to a level belowdetection. In one embodiment, the target gas comprises ambient airincluding methane in a concentration of at least 1.8 ppm.

The term “ambient air” as used herein is without limitation urban air,countryside air, indoor air, industrially emitted air, process exhaustair, air inside closed spaces (inside cars, busses, trucks, taxis,etc.), air in semi-enclosed spaces (bus stops, train stations, parkinghouse, etc.), air emitted from traffic or ships, air emitted throughconstruction site process, air emitted from biogenic or natural sources,air found within the Earth's atmosphere, air unable to escape theEarth's gravity. The ambient air also includes “ambient polluted air”which means ambient air with high concentrations of VOCs, such asmethane, above 1.8 ppm. Such ambient polluted air is typically found inlivestock barns, fugitive emissions, fracking sites, leaking orabandoned wells, waste dumps, wetlands etc.

As described herein the target gas is typically ambient air, such asambient polluted air, but may also be a different target gas exhaustedfrom a chemical facility or other industrial site and contain agentsthat destroy the halogen gas. In such circumstances the reaction chamberis constructed with a prefilter that is adapted to remove such agentsbefore being exposed to the halogen gas.

When the reaction chamber is in use and ambient air is transportedthrough the chamber, it is often suitable to have a prefilter to removeairborne particulate matter from the target gas before being exposed tothe halogen gas. The target gas, such as ambient air, may be transportedthrough the reaction chamber by passive means, such as due to the aircirculation and/or wind conditions, or may be transported through thechamber via a fan or by using a pump means.

When the concentrations of VOC in the target gas are below thecombustion limit, they are typically below 4.4%, such as between 1.8 ppmand 4.4%.

When the concentrations of VOC in the target gas are above the lowercombustion limit, they are typically above 4.4%, but below the upperflammable limit typically 16.4% In order to remove VOCs, such asmethane, in the target gas, such as ambient air, even smallconcentrations of halogen gas may be suitable, that is concentrationsbelow the stoichiometric level in relation to the VOC concentration inthe gas or a concentration sufficient to maintain reactivity via thecatalytic halogen recycling method, since such concentrations of halogengas will remove VOCs from the target gas. Typically, and in order toremove all VOCs, the halogen gas concentration is present in an amountwhich is at least at the stoichiometric level in relation to the VOCconcentration in the gas. Higher concentrations of halogen gas may beused to make certain that all traces of VOCs are removed.

Halogen gas is known to be chlorine, bromine, fluorine, and iodine gas,and consequently, the removal of VOCs, such as methane according to thepresent invention leads to formation of HCl, HBr, HF and HI,respectively.

When chlorine is used as halogen gas, the method of the presentinvention generates HCl, which is advantageous in livestock settingsbecause it helps to trap ammonia in the liquid phase, decreasing ammoniaemissions. The wastewater exiting the system can be used in the slurrywaste as fertilizer or for biogas production.

The method of the present invention is carried out in a suitablereaction chamber, having an inlet for receiving the target gas, areaction zone wherein the target gas is reacted with halogen radicals toremove the VOC concentrations and an outlet providing the target gaswith the removed concentration of VOC. The generation of hydrogen halidegas, unreacted chlorine, formaldehyde, and carbon oxides makes itpreferable to have a filter such as a scrubber in the reaction chamberbefore the outlet. The filter is adjusted to remove hydrogen halide,unreacted chlorine, formaldehyde, and carbon oxides, and may be selectedfrom the group consisting of a trickling filter, active carbon filter, agas adsorbing filter, an electrostatic filter, a honeycomb filter, asponge based filter, a fabric filter, or a catalyst to further removeVOC concentrations, or a photocatalyst, or a trickling scrubber filter.

A further embodiment includes a functionality whereby the halogenmaterial is recycled. For example, HCl and HOCl are collected in thescrubber (e.g. a police filter to remove HCl made of activated charcoalor another suitable material) and react to form Cl₂ which is used againin the reaction chamber. The yield of HOCl can be enhanced by addingozone. The performance can be improved using a countercurrent flow. Thisembodiment decreases use of halogen and emission of halogen.

To optimize the reaction taking place it is preferable to add ozone intothe reaction chamber which ozone reacts with halogen species inoxidation state (−1) to create volatile and/or photolabile halogenspecies, the mechanism thereby becoming catalytic in halogen. The ozoneis introduced into the reaction chamber through the inlet or through anopening in the reactor wall into the reaction zone.

FIG. 1 shows an embodiment of the device of the present invention (10),such as a photochemical air purification device of a cylindrical shape(20). Air comprising the target gas for example methane enters throughan inlet (12) of the device (10), further into the reaction zone (22)through a catalyst, filter and/or scrubber (24) and out via outlet (28).The target gas will react with chlorine gas in the reaction zone (22)when lamps (14) photolytically generates chlorine radicals, here shownas an array of LED lamps (14). The chlorine gas is injected (16) intothe reaction chamber upstream the reaction zone and flows to thereaction zone (22) for generation of chlorine radicals as describedabove. The chlorine radicals will then react with the methane in thetarget gas to remove said methane from the target gas. Byproducts areremoved by a catalyst, filter and/or scrubber (24). A sensor (18) formeasuring gas concentrations is located upstream of the LED array (14)and another similar sensor (26) is located downstream of the catalyst,filter and/or scrubber (24).

FIG. 2 shows an embodiment of the device of the present invention (30),such as a photochemical air purification device of a tank type shape.Air comprising the target gas is let through an inlet (32) of the device(30), further into the reaction zone (60) through scrubber media (42)and out via outlet (34). The tank holds a sump (36) in the bottom. Thetarget gas will react with chlorine gas let in via inlet (46) and ozonegas via inlet (46) in the reaction zone and LED lamps (50) willphotolytically generate chlorine radicals. Ozone is added to the reactorchamber to promote the formation of HOCl. Lamps (48) are for photolyticgeneration of chlorine radicals in the scrubber (42). The chlorineradicals will then react with the methane in the target gas to removesaid methane from the target gas. At the top of the tank a nozzle (40)for spraying water led in from the top via a container (52) holdingwater provided from at water supply (56). Recirculation of chlorine gasfrom the bottom of the tank (54) using a pump (38) and to the watercontainer (52). A Sensor (58) for measuring gas concentrations, physicalconditions etc. is located in the chamber above the scrubber media (42).Another Sensor (60) for measuring gas concentrations, physicalconditions etc is located in the chamber below the scrubber media (42).

FIG. 3 shows an embodiment of the device of the present invention (60)in line with ventilation system, for use in livestock barn (62). Thechimney is an integrated part of the roof (64) and comprises the deviceof the present invention. Air comprising target gas (80) from the barnis let through the ventilation system/chimney comprising the device ofthe present invention. A fan (76) drives the air through the chimneyfrom the inlet (74) where chlorine gas is provided and the air flows upto the reaction zone (70) where the chlorine gas is exposed to UV lightfor example light from LED lamps (72) to initiate chlorine radicalformation. The chlorine radicals will then react with the methane in thetarget gas to remove said methane from the target gas and residual gasis let through a catalyst, filter and/or scrubber (82) and further outvia chimney top outlets (66). A sensor for measuring gas concentrations,physical conditions etc. is placed both at the top part (68) and at thebottom part (78) of the chimney.

FIG. 4 shows an embodiment of the device of the present invention (90)for capturing and destroying methane from fugitive sources, such as leakfrom ground, garbage dump, sewer, abandoned well or mine. The methanedestruction system (90) has a with skirt (92) which covers the groundand is adapted to collect methane emissions (114). The device (90) isequipped with feet to support the device (94, 96, 98). A fan (100) movesincoming target gas/air (102) from a fugitive source up through thechimney (inner volume of the device). The target gas moves into thereaction chamber and further to a reaction zone where the chlorine gas,introduced from a source (104) into the reaction chamber is exposed toUV light for example light from LED lamps (108) to initiate chlorineradical formation in the reaction zone. The chlorine radicals will thenreact with the methane in the target gas to remove said methane from thetarget gas and residual gas is let through a catalyst, filter and/orscrubber (110) located downstream from the reaction zone and further outvia chimney top (112) and vented to atmospheres (116). A sensor formeasuring gas concentrations, physical conditions etc. is placed both atthe top part (120) and at the bottom part (106) of the chimney.

FIG. 5 shows an embodiment of the device of the present invention (150)for capturing and destroying methane from ambient air being led throughinlet (152). A fan (154) moves incoming target gas/air (152) from theambient air up through the chimney (inner volume of the device). Theambient air moves into the reaction chamber and further to a reactionzone where the chlorine gas, introduced from a source inlet (164) intothe reaction chamber and ozone introduced from a source inlet (162) intothe reaction chamber is exposed to UV light for example light from LEDlamps (156, 158) to initiate chlorine radical formation in the reactionzone. The chlorine radicals will then react with the methane in thetarget gas to remove said methane from the ambient air and residual airis let out via chimney top (174) and vented to atmospheres (170). Theozone is added to the reactor to promote the formation of HOCl. A sensorfor measuring gas concentrations, physical conditions etc. is placedboth at the top part (178) and at the bottom part (176) of the chimney.At the top of the device (150) in the reaction chamber a nozzle (168) islocated, for spraying water led in from the top via a water solutionreservoir (160). There is a recirculation of water from the bottom ofthe device to the water reservoir (160) via a pump (166) through a tubeto the nozzle (168).

FIG. 6 illustrates one preferred system of the present invention havinga device of the present invention and performing the process of thepresent invention. The oxidation of HCl can be done by the bleachreaction HCl+HOCl—->Cl₂+H₂O, but it is preferred to oxidize HCl usingthe Deacon Reaction: 4HCl+O₂—->2Cl₂+2H₂O. Catalysts exist to speed thisprocess, the latest generation is based on ruthenium(IV) oxide developedby Sumitomo Corp. Earlier processes include Kel-Chlor, Shell-Chlor andMT-Chlor. The Deacon reaction is a preferred alternative to the bleachreaction. FIG. 6 shows an overview of a high intensity process of thepresent invention. The airstream containing methane enters from lowerright. Cl₂ gas is added and photolyzed by UV LED lamps to producechlorine radicals which react with methane yielding HCl. HCl isextracted using a scrubber and converted to chlorine gas (Cl₂) by theDeacon reaction. This chlorine gas is then recycled. In addition, thereis some Cl₂ present in the waste gas stream which is trapped usingcondensation as shown. As shown, air is entering the system to form pureoxygen for use during the Deacon reaction. This is a preferredalternative to using pure atmosphere, which is a possibility. Further asshown, Cl₂ is extracted from the waste air stream by liquefaction.Thermal management involving a heat exchanger will improve theefficiency of this process. It is necessary to remove water vapor fromthe air first before Cl₂ can be removed.

FIG. 7 illustrates one preferred system of the present invention wherethe Deacon reaction operates on the entire airstream, thus eliminatingthe need for the scrubber. In addition to eliminating the scrubber, thismodification would eliminate the extractive rectification andpotentially also the pressure swing adsorption purification of oxygen.

FIG. 8 shows the choice of LED wavelength and as seen the absorptioncross section of chlorine increases from 400 to 320 nm, however, LEDlights become increasingly expensive as wavelength decreases. An optimumphotolysis wavelength is achieved around 365 nm in the range 300 nm to400 nm.

FIG. 9 illustrates another preferred system of the present inventionwhich is the inclusion of a second scrubber to regenerate Cl₂. Inrespect of reduced energy input, the Deacon reaction and cooling is abetter choice.

FIG. 10 illustrates a model of the photochemical reactions taking placeduring the use of the device, process and system of the presentinvention. The formation of chlorinated methane derivatives wasdetermined to be very small and of no concern. The main product ofmethane oxidation will be carbon monoxide. This may be undesirable, andtherefore it may be useful to convert it to CO₂ using a catalyst. Avariety of catalysts are available for this purpose such as a supportedplatinum or palladium catalyst, alternatively rhodium and ruthenium.

Below are described some specific embodiments. The first is a gas phasereactor with an optional system for trapping products. The second is anintegrated heterogeneous reactor with chlorine cycling. Note thatchlorine compounds in the gas and aqueous phases are corrosive, and caremust be taken to choose materials that are compatible with thechemistries of the reactors. For example, glass and many types ofplastic are inert.

A Gas Phase Photochemical Reactor Based on Chlorine Atoms.

The method consists of these steps: waste air is assumed to be flowingthrough a channel.

-   -   1. Introduction of Chlorine Precursor.

A suitable precursor is a molecule that can be photolyzed to producechlorine atoms (Cl), such as chlorine gas (Cl₂). Chlorine gas can bepurchased, or it can be produced cheaply and easily on site in the smallquantities that are required by the process using electrolysis ofsaltwater [Harnung and Johnson 2012]. Other gases containing chlorinethat can be photolyzed could also be used.

-   -   2. Activation of the Chlorine Precursor to Produce Chlorine        Atoms.

Preferred method is photolysis such as

-   -   Cl₂+hv→2Cl⁻

The light source is any light capable of photolyzing the precursor suchas the sun, for example LED lamp, fluorescent lamp, discharge lamp,incandescent lamp, laser. The wavelength of light (‘hv’ represents aphoton) is shorter than 550 nm, ideally UV light with a wavelengthshorter than 400 nm for example a LED at 360 nm.

This is followed by reaction of the chlorine atom with the pollution, incase of methane:

-   -   Cl⁻+CH₄→HCl+CH₃ ⁻

More in General:

-   -   Cl⁻+RH→HCl+R⁻        where RH represents a pollutant hydrocarbon with a hydrogen atom        H and the rest of the molecule called ‘R⁻’, R⁻ and H together        comprising methane, benzene, capric acid, etc., etc. After        initial attack by Cl⁻, the molecular fragment R will proceed to        react with atmospheric molecular oxygen O₂ and other oxidizing        species present in the system; the key to initiating this        cascade of reactions is the initial attack by Cl⁻.    -   3. The Oxidised Material is Removed from the Air Stream.

This could be performed using a particle filter such as a fiber filter[Ardkapan 2014] or electrostatic precipitator [Kwiatkowski 2019]. Apreferred embodiment is a wet scrubber because it can trap particles,acting as a diffusion battery, and also trap acids such as thehydrochloric and organic acids produced in the photochemical reactions,due to their affinity for the aqueous phase.

Second Chlorine Cycling Using a Scrubber (Heterogeneous Reactor,Countercurrent Flow, Packed Bed) Photoreactor.

The scrubber chamber is packed with objects capable of dispersing theflow of the aqueous phase, increasing surface area and area of contactbetween the fluid and air, and not blocking the UV light, such aspurpose-designed beads or Raschig rings of inert material. The aqueousphase flows downward through the bed, for example from a nozzle actingas a showerhead at the top of the reactor. The air stream flows up frombelow or from the side. UV lights are attached around the outside of thereactor. Chlorine is introduced to initiate the process.

For example, using chlorine gas,

-   -   Cl₂+hv→2Cl⁻        And, in presence of methane:    -   Cl⁻+CH₄→HCl+CH₃ ⁻        this reaction is a specific example of the general form:    -   Cl⁻+RH→HCl+R⁻        Successively, the radical formed reacts with oxygen in the        following way:    -   R⁻+O₂+M→RO₂ ⁻ +M

Where ‘M’ is a molecule from the atmosphere that acts as a collisionpartner. The system will produce RO₂ ⁻ and HO₂ ⁻ due to known processes(e.g., RO⁻ and the single carbon atom form CH₃O⁻ lead to RO₂ ⁻ and HO₂ ⁻formation), leading to ClO⁻ formation

-   -   Cl⁻+HO₂ ⁻→ClO⁻+OH⁻    -   Cl⁻+RO₂ ⁻ →ClO⁻+RO⁻        ClO would then react with HO₂ ⁻ Forming HOCl and oxygen:    -   ClO⁻+HO₂ ⁻ →HOCl+O₂        HOCl and HCl dissolve easily in water:    -   HOCl(g)→HOCl(aq) HCl(g)→HCl(aq)        Where they react to reform Cl₂:    -   HOCl+HCl→Cl₂+H₂O

This reaction completes the cycle allowing the chlorine to be recycled.If the conditions permit it, the electrolysis of the aqueous media whereHOCl and HCl are dissolved may further increase the production ofchlorine gas.

These reactions are listed to illustrate the main features of thechemical process and are not intended to limit the invention in any wayor be an exhaustive list.

Further, since the aqueous phase is moving downward, while the pollutedair is moving upward, this will act to conserve chlorine within thesystem improving catalytic efficiency and reducing cost and escape ofchlorine. Optionally, a second scrubber or filter may be added after theheterogeneous reactor/scrubber as a police filter to capture chlorinespecies.

Ozone may be added to the reactor to promote the formation of HOCl, inorder to maintain the HCl to HOCl stoichiometry to optimize recycling ofchlorine.

The aqueous phase will flow into and through the scrubber and collect atthe bottom where it may be drained or pumped into a reservoir, fromwhich it may be drained, or pumped to the top of the system torecirculate through the scrubber. It will be necessary to renew thisfluid either by changing it at certain intervals, or by continuallyintroducing a slow flow of water into the system; wastewater can bedrained into the municipal water system provided it meets requirementsas regards impurity levels, etc. Alternatively, it could be used toenhance the acidity of a biogas generation system for example usinganimal waste on a farm. Chlorine will be added slowly to the system tocompensate for loss to the gas and aqueous phases.

A control system will regulate addition of water, chlorine, UV light,air flow, pumping. There is a powerful recycling effect when ozone isintroduced to the system. It means that only a little chlorine and lightare used to initiate the process, and then ozone can be used to maintainit, further improving performance and saving energy, and decreasingchlorine emissions.

Livestock Barn Embodiment

The new system as illustrated in FIG. 6 uses a livestock barn scenarioto determine performance.

This may be built as a prototype to demonstrate the effectiveness.

Conditions of 60,000 m³/hr (17 m³/s) and 50 ppm of methane.

Preferred Conditions:

-   -   Residence time of 5 to 20 seconds    -   Volume of 100 to 400 m³    -   Chlorine photolysis rate of 0.1 to 10 s⁻¹    -   Chlorine concentration of 100 to 50,000 ppm    -   Performance >90% removal of methane preferably >95%    -   Total power 50 kW.

Mineshaft Embodiment

The feasibility study focuses on exhaust air from a mineshaft with aflow of 150 m³/s, temperature of 40° C., 100% relative humidity, methanemole fraction of 5000 ppm.

The preferred system requires 15 s residence time corresponding to avolume of 2250 m³, a photolysis rate of 0.2 s⁻¹ and 8750 ppm of Cl₂, LEDlighting, the ruthenium oxide catalyzed process developed by SumitomoCorp., for recovering chlorine, thereby achieving 99% conversion ofmethane with a power input of 14.6 MW. The energy input could further bereduced to ca 11.9 MW depending on modifications to the ruthenium oxidecatalyzed process developed by Sumitomo Corp., or reduced through moreefficient cooling.

Preferred Ranges in Above Embodiment are:

Residence time 5 to 25 s Chlorine photolysis rate 0.1 to 10 s⁻¹ Chlorineconcentration 100 to 50,000 ppm Performance >90% removal of methanepreferably >95%

All references, including publications, patent applications and patents,cited herein, are hereby incorporated by reference to the same extent asif each reference was individually and specifically indicated to beincorporated by reference and was set forth in its entirety herein.

All headings and sub-headings are used herein for convenience only andshould not be construed as limiting the invention in any way.

Any combination of the above-described elements in all possiblevariations thereof is encompassed by the invention unless otherwiseindicated herein or otherwise clearly contradicted by context.

Recitation of ranges of values herein are merely intended to serve as ashort method of referring individually to each separate value fallingwithin the range, unless otherwise indicated herein, and each separatevalue is incorporated into the specification as if it were individuallyrecited herein. Unless otherwise stated, all exact values providedherein are representative of corresponding approximate values (e.g., allexact exemplary values provided with respect to a particular factor ormeasurement can be considered to also provide a correspondingapproximate measurement, modified by “about”, where appropriate).

All methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext.

The terms “a” and “an” and “the” and similar referents as used in thecontext of describing the invention are to be construed to insert boththe singular and the plural, unless otherwise indicated herein orclearly contradicted by context. Thus, “a” and “an” and “the” may meanat least one, or one or more.

The term “and/or” as used herein means each individual alternative aswell as the combined alternatives, for instance, “a first and/or secondbarrier” is intended to mean one barrier alone, the other barrier alone,or both the first and the second barrier at the same time.

The use of any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise indicated. No language in the specification should beconstrued as indicating any element is essential to the practice of theinvention unless as much is explicitly stated.

Throughout the description when “selected from” or “selected from thegroup consisting of” is used it also means all possible combinations ofthe stated terms, as well as each individual term.

The citation and incorporation of patent documents herein is done forconvenience only and does not reflect any view of the validity,patentability and/or enforceability of such patent documents.

The description herein of any aspect or embodiment of the inventionusing terms such as “comprising”, “having”, “including” or “containing”with reference to an element or elements is intended to provide supportfor a similar aspect or embodiment of the invention that “consists of”,“consists essentially of”, or “substantially comprises” that particularelement or elements, unless otherwise stated or clearly contradicted bycontext (e.g., a composition described herein as comprising a particularelement should be understood as also describing a composition consistingof that element, unless otherwise stated or clearly contradicted bycontext).

This invention includes all modifications and equivalents of the subjectmatter recited in the aspects or claims presented herein to the maximumextent permitted by applicable law.

The features disclosed in the foregoing description may, both separatelyand in any combination thereof, be material for realizing the inventionin diverse forms thereof.

Each and every embodiment as described in connection with the differentaspects also applies to the further aspects described above, bothindividually and in combination.

Specific Embodiments of the Invention Livestock Barn

Elevated methane concentrations are commonly seen in the exhaust airfrom barns, for example barns for milk cows, cattle, pigs, chickens andother livestock. This embodiment, shown in FIG. 3 , is fitted into theexhaust system, providing a simple, low-maintenance, low-cost method ofdestroying methane. For example Cortus et al. [Cortus 2015] found adairy cow emits 390 g of methane per day. For a barn with 300 cows and aventilation of 1500 m³/hour/cow means a methane concentration of 16 ppmin the exhaust air. Such a barn may have a number of ventilator unitseach with a capacity of 10,000 to 20,000 m³/hr of air. This is a simpledirect chlorine reactor, which could optionally be fitted with ascrubber and chlorine recycling system.

Symbol Unit Value Name Q m³/hr 20000 volume flow r_m(Cl) m(Cl atoms)g/hr 2000 rate of addition of Cl d m 1 Diameter of tube x(CH₄) ppm 16methane mixing ratio x(VOC) ppm 20 VOC mixing ratio P W 3000 Power ofdiode at 360 nm l m 3 length of photolysis region v m/s 7 flow velocity

Fugitive Emissions

Methane is released from sources such as leaking natural gas pipelines,coal seams, leaking storage reservoirs, melting permafrost, andlandfills. This embodiment (FIG. 4 ) collects air from these fugitiveemission sources and destroys the methane and odor. Portable, for atemporary installation.

Symbol Unit Value Name Q m³/hr 1000 volume flow r_m(Cl) m(Cl atoms) g/hr50 rate of addition of Cl d m 1 Diameter of tube x(CH₄) ppm 10 methanemixing ratio x(VOC) ppm 5 VOC mixing ratio P W 250 Power of diode at 360nm l m 1 length of photolysis region v m/s 1 flow velocity

Industrial Scrubber

An industrial setting may place greater demands on an emissions controlsystem, to reduce emissions of byproducts. A permanent installation(FIG. 5 ) can justify a system with better performance; therefore, thisunit includes a scrubber to trap HCl emission and recycle the chlorine.

Symbol Unit Value Name Q m³/hr 5000 volume flow r_m(Cl) m(Cl atoms) g/hr250 rate of addition of Cl d m 1 Diameter of tube x(CH₄) ppm 10 methanemixing ratio x(VOC) ppm 5 VOC mixing ratio P W 750 Power of diode at 360nm l m 2 length of photolysis region v m/s 2 flow velocity

Test Prototype

A portable system (such as shown in FIG. 1 or FIG. 2 ) to use in thelaboratory for optimization and to bring on-site to test feasibility.

Symbol Unit Value Name Q m³/hr 500 volume flow r_m(Cl) m(Cl atoms) g/hr25 rate of addition of Cl d m 1 Diameter of tube x(CH₄) ppm 10 methanemixing ratio x(VOC) ppm 5 VOC mixing ratio P W 100 Power of diode at 360nm l m 1 length of photolysis region v m/s 0.5 flow velocity

Ambient Air Cleaning

There is significant interest in a system that could remove methane fromair at ambient concentrations.

Symbol Unit Value Name Q m³/hr 10000 volume flow r_m(Cl) m(Cl atoms)g/hr 75 rate of addition of Cl d m 2 Diameter of tube x(CH₄) ppm 2methane mixing ratio x(VOC) ppm 1 VOC mixing ratio P W 400 Power ofdiode at 360 nm l m 3 length of photolysis region v m/s 0.9 flowvelocity

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1-19. (canceled)
 20. A method for removing VOC, such as methane,concentrations in a target gas comprising VOC, the method comprising,optionally in a suitable reaction chamber, exposing the target gas to ahalogen radical precursor, such as a halogen gas, and a light from asuitable light source having a wavelength sufficient to activate thehalogen radical precursor to halogen radicals, wherein the halogenradicals react with the VOC in the target gas to provide the target gaswith a removed concentration of VOC.
 21. The method of claim 20, whereinthe VOC in the target gas is selected from a primary and/or secondaryradiative forcing agents (greenhouse gases), such as hydrocarbons, inparticular methane.
 22. The method of claim 20, wherein the target gaspolluted with VOC is ambient polluted air, air in livestock barns,fugitive emissions etc.
 23. The method of claim 20, wherein the halogengas is selected from chlorine and bromine gas, in particular chlorinegas, where chlorine gas is purchased or produced on site usingelectrolysis of saltwater or is part of other gases containing chlorinethat can be photolyzed.
 24. The method of claim 20, wherein thewavelength is from 540-180 nm, such as 400-300 nm, for instance 380-320nm, in particular from 370-350 nm.
 25. The method of claim 20, whereinthe light source is selected from a fluorescent lamp, an LED lamp, anincandescent lamp, a gas discharge lamp, sunlight, or combinationshereof.
 26. The method of claim 20, wherein the concentrations of VOC inthe target gas are below the combustion limit.
 27. The method of claim26, wherein the VOC comprises methane in a concentration from 1.8 ppm to5% (50000 ppm).
 28. The method of claim 20, wherein the concentrationsof VOC in the target gas are above the combustion limit.
 29. The methodof claim 20, wherein the halogen gas concentration is present in anamount which is at least at the stoichiometric level in relation to theVOC concentration in the gas.
 30. The method of claim 20, wherein thegas with the removed concentration of VOC, such as methane, istransported through a filter or scrubber to decrease or remove halogenacid, e.g., HCl, unreacted chlorine, formaldehyde, CO, CO2.
 31. Themethod of claim 20, wherein the suitable reaction chamber is present andhas an inlet for receiving the target gas, a reaction zone wherein thetarget gas is reacted with halogen radicals to remove the VOCconcentrations, optionally a system to increase the light source pathway(e.g. mirrors), optionally a filter or scrubber, and an outlet providingthe target gas with the removed concentration of VOC.
 32. The method ofclaim 20, wherein fluid ozone, e.g. gas ozone, is added into thereaction chamber in a suitable concentration to convert halogenic (orother halogen species in oxidation state I) to volatile and/orphotolabile halogen species.
 33. The method of claim 20, whereinelements of the target gas that may harm the device or destroy thehalogen gas are removed before being exposed to the halogen gas.
 34. Themethod of claim 20, wherein the target gas is led through a prefilter toremove larger particles from the target gas before being exposed to thehalogen gas.
 35. The method of claim 20, wherein the reaction chamber ispresent, and the chamber comprises two compartments, one first reactioncompartment and a second compartment, a filter/packed bed separating thefirst and second compartment, wherein the target gas after reaction inthe first compartment is transported through the filter/packed bed intothe second compartment wherein the target gas with the removedconcentration of VOC is exposed to water which reacts with halogenicacid to form halogen that is recycled to the reaction compartment.
 36. Adevice for removing VOC concentrations in a target gas comprising VOC,wherein the device comprises a) a reaction chamber for exposing thetarget gas to a halogen gas and a light from a suitable light sourcehaving a wavelength sufficient to activate halogen gas to halogenradicals; b) an inlet for receiving the target gas; c) an outlet forproviding the target gas with a removed concentration of VOC; d) a lightsource for providing a wavelength sufficient to activate halogen gas tohalogen radicals; and e) optionally a filter and/or scrubber fordecreasing or removing halogen acid, e.g., HCl, unreacted halogen, e.g.,chlorine, formaldehyde, CO, CO2 before the target gas with the removedVOC concentrations leaves through the outlet.
 37. The device of claim36, comprising a recycle element for recycling halogen gas regeneratedfrom the halogen acid gas formed during the reaction, to the reactionchamber.
 38. A method for removing VOC concentrations in a target gascomprising VOC, comprising introducing said target gas into the deviceof claim 36.